Abstract: Flexible electronic devices have attracted great interest owing to the advantages of flexible substrates as well as its arbitrary surface geometries, which may be one key branch of next-generation electronic devices, including paper-like electronic displays, light-emitting diodes, biointegrated medical devices, and solar cells. In recent years, some researchers have combined flexible techniques with spintronics to explore the effect of strain on magnetoelectric heterojunctions grown on flexible substrates and to control the magnetic and electric properties by changing the curvature of the substrate. These studies pave the path for the designing electronic devices, including magnetic storage devices, magnetic sensors, and non-volatile resistance memory.
Abstract: To study the changing law of rock mechanics under different water conditions and to ensure that the water content was the sole factor, sandstone was used as the experimental material. Three different kinds of rock samples were prepared with different moisture states whose average saturation coefficients were 2.82%, 52.11%, 100%, i. e., dry, semi-saturated, and saturated. The mechanical properties of the rocks were dynamically tested under the action of static load and eight kinds of impact energy. The experimental results reveal that under static load, compared with dry rock, the stress-strain curves of half-saturated and saturated rock samples show decreasing peaks with increasing water content, and their compressive strengths decrease by 8.12% and 19.26%, respectively. Under dynamic loading, with increases in strain rate, the strengths of the three samples show a linear change in different degrees, the stress-strain curves shift to the right, and the peak values increase. The dry and water-bearing rocks exhibit two obviously different trends in the unloading stage, especially in the second stage of unloading. Also, under the same impact energy, as the water content of the rock increases, the degree of fragmentation also increases.
Abstract: Based on uniaxial compression laboratory results, the failure process of marble with a single hole was simulated using the particle flow code PFC2D under uniaxial and biaxial compressions. The influence of the pre-existing hole shape, confining pressure and the rock heterogeneity on the mechanical properties of marble and the coalescence of cracks was analyzed. Numerical results show that compared to an intact marble specimen, the peak strength of a specimen containing a single hole reduces significantly, and the extent of reduction is related to the hole shape. The confining pressure has a significant effect on the mechanical properties of marble and the coalescence of cracks. The peak strength increases with the increase of confining pressure, while the peak deviator stress increases first and then decreases with the confining pressure increasing. Specimens containing circular holes exhibit X-type shear failure, while specimens containing rectangular or U-shaped holes exhibit diagonal shear failure. The mineral nodules in the rock specimen significantly affect the propagation of cracks leading to a change in the failure mode of marble specimen. Analysis results of the microscopic mechanisms show that the initiation and propagation of cracks around the hole is always accompanied by the release and transfer of stress from a concentrated zone. Three types of macroscopic cracks can be classified in specimen containing a single hole as hole surface spalling, tensile crack, and compressive shear crack.
Abstract: To study the fractal characteristics of stylolite and its influence on the strength of limestone, the fractal dimension of horizontal stylolite and vertical stylolite was analyzed using the power spectral density method and the digital image box dimension method based on digital image processing technology. The influence of the stylolite on the limestone strength and the crack evolution process of the limestone were studied through experimental tests and numerical simulations. The results show that the fractal dimension of stylolite lies between 1 and 2, indicating that the stylolite is a self-affine fractal structure in nature, and the vertical stylolite has a large roughness. The stylolite weakens the strength of limestone by about 20% on average, the strength of limestone with different inclinations of stylolite shows less obvious anisotropy and stylolite has negligible effect on the elastic modulus of limestone. In the failure process of limestone, crack initiation and propagation in limestone is closely related to the stylolite, and the stylolite accelerates the damage and failure of the limestone. Numerical simulations show that the thickness, position, numbers, and fractal dimension of the stylolite have significant effect on the strength of the limestone.
Abstract: In this study, the mineral composition and embedded features of the nickel slag as well as its phase transformation in a settlement furnace during deep reduction were investigated through chemical composition analysis, X-ray diffraction, optical microscopy, scanning electron microscopy, and energy dispersive spectrometry. The results show that the phase composition of slag includes hortonolite and glass. The Cu-Ni-Fe sulfide mineral is distributed in the silicate irregularly, and the sulfide material is too small to reclaim. The nickel slag transforms into akermanite, ferronickel, augite, cancrinite, riebeckite, and quartz by deep reduction. The process is characterized by constant mineral components of reduzate, and the contents of akermanite and ferronickel are the most when heated to 1300℃. The reduction time is also an important factor during the process, and the contents of ferronickel increase over time, maximizing at 120 min. The thermodynamic analysis shows that the main reaction performed during the reduction is that olivine and calcium oxide transform into akermanite and FeO, and then the FeO is reduced to iron by C and CO. The metal sulfides, calcium oxide, and C are transformed into copper and nickel and then dissolved in the iron, and the CaS then crystallized out with the silicate minerals.
Abstract: The floatability of hematite and quartz were investigated using dodecylamine as collector and cassava starch, carboxymethyl starches with degree of substitution (DS) of 0.026 and 0.21, and phosphate ester starches with DS of 0.0065 and 0.055 as depressants. The effect of DS on the depressing behavior of modified starches was studied. The flotation results show that native starch, carboxymethyl starch with DS of 0.026, and phosphate ester starch with DS of 0.0065 can strongly depress hematite, whereas carboxymethyl starch with DS of 0.21 and phosphate ester starch with DS of 0.055 weakly depress it. The native starch and carboxymethyl starch with DS of 0.026 can strongly depress quartz, whereas the other three starches are investigated possessed less depressing capabilities for quartz. The results reveal that a low-DS phosphate ester starch is a highly selective depressant in the reverse flotation of silica-containing iron ore with cationic collectors. The Zeta potential measurements exhibit that modified starches with higher DS can lead to lower Zeta potentials of minerals. Thus, the weakened depressing capabilities of modified starches might adsorb cationic collectors on the mineral surface via electrostatic attraction with negatively charged groups stretching into the solution.
Abstract: The process of separation of slag and alloy and distribution of vanadium in casting slag during the casting process of multiperiod FeV50 preparation were analyzed using the principle of infinite fluid gravitational settling. The effects of slag viscosity, particle size, casting temperature, molten-slag thickness, and insulation system on total vanadium (TV) content in slag were investigated. The analysis demonstrates that vanadium mainly comprises vanadium oxide and incompletely deposited primary ferrovanadium alloy in the casting slag. The sedimentation rate of settlement alloy increases with an increase in the particle size and decreases with an increase in the slag viscosity. The dropping time of FeV50 alloy and floating time of molten slag is 24.9 and 1.2 min, respectively, when the casting conditions are as follows-casting temperature:1850℃, slag layer thickness:50 mm, particle size:100 μm, and slag composition mass fraction:65.2% Al2O3, 15.5% CaO, 14.6% MgO, 1.9% Fe2O3, and 0.9% SiO2. Through optimization experiments, the average vanadium mass content in the slag is reduced from 1.39% to 0.58% for the following casting conditions-slag layer thickness:35 mm, casting temperature:1900℃, slag component:60%-65% Al2O3, 15%-20% CaO, 9%-15% MgO; and casting insulation thickness:9 cm.
Abstract: A new technique termed surface electromagnetic pulse refining was developed for improving the solidified structure of a 7A04 aluminum alloy DC-casting. The effect of the pulsed electromagnetic field on the solidified microstructure and properties of the alloy was investigated. From the viewpoint of potential energy, the dynamics of forming nucleus and the grain motion were theoretically predicted based on the concepts of the action of the pulsed electromagnetic energy on the melt or particles. The experimental results indicate that the solidified structures are modified by the electromagnetic pulse from rose-like structures to globular structures with a fine grain size. The grain size in the edge zone and central zone of the billet is decreased by 22.7% and 14.2%, respectively, and the strength and plasticity of the alloy are also increased. The grain refinement can be explained by the nucleation rate increases, because the electromagnetic energy helps to decrease the critical Gibbs free energy of the system. In addition, the electromagnetic pulse appears to increase potential energy of the primary α-Al, which quickly attains a steady state in the melt.
Abstract: The thermal regime and structural control between continuous caster offline and a reheat furnace has a significant impact on the cracking problem occurring during hot charging or hot rolling. The effect of the charging process on the characteristics of austenite transformation and sizes of reheated grains was experimentally analyzed using thermal simulation. The in situ observation results using a high-temperature confocal laser scanning microscope shows that film-like ferrite and Widmanstätten ferrite are present along the grain boundary with amounts of retained austenite when hot charged at 700℃ in the dual phase region for J55 steel, and the size and location of the austenitic grain remain constant after reheating to 1200℃. When warm charged at 600℃ in the single phase region, large amounts of ferrite and pearlite are observed, and austenite grains are clearly refined after reheating to 1200℃. It is also found that the austenitic grain can only be visibly refined when the transformed ferrite fraction is higher than 70% for SS400 steel hot charged at different temperatures using a muffle furnace. The grain refinement is more obvious when the transformed ferrite fraction is higher than the critical value.
Abstract: The effects of cyclic heat treatment and hot deformation on the spheroidization and orientation of the TC17 titanium alloy were investigated using a light microscope (LM) and electron backscattered diffraction (EBSD). The experimental results indicate that in the two-phase temperature range of a simple, cycle heat treatment, the spheroidization of the lamellar microstructure of the TC17 titanium alloy is finite. After cyclic heat treatment and compression deformation, the Widmannstatten structure disappears, the spheroidized α lamellae is more obvious, but the uniformity of its orientation is not greatly improved. In addition, the recrystallization velocity, and the strength and toughness of the two phases in deformation lead to a difference in their orientation, and the recrystallization velocity of the α phase is faster than that of the β phase. In the deformation process, the anisotropy of the α phase is preferentially reduced. On the other hand, during the hot deformation process, the degree of deformation of the α phase is lower than that of the β phase, because the α phase is harder than the β phase. The strain is primarily concentrated on the softer β phase adjacent to α phase, which produces greater uniformity in α phase than in the β phase.
Abstract: To investigate the microstructure transformation and the change of the dimensional accuracy of the hot blanking parts, the hot blanking experiments for B1500HS steel were performed with different temperatures and die clearance ratios. The effects of blanking temperature on the phase transformation and mechanical properties of steel were analyzed using the cooling curves. The effects of blanking temperature and die clearance ratio on the dimensional accuracy of the hot blanking parts were analyzed based on the measured diameter of the parts. The fracture morphology of the parts was observed, and the effect of blanking temperature on the fracture quality was analyzed. The results show that, with decreasing die clearance ratio, the diameter of the blanking parts increases at the same blanking temperature. When the die clearance ratio remains constant with decreasing blanking temperature, the dimension deviation of the parts has a fluctuation tendency of "positive growth-negative growth-positive growth". The blanking parts have a higher accuracy as the blanking temperature is in the range of 600-650℃ or 750-800℃. While increasing the blanking temperature, the micro-hardness of the parts increases. The microstructure of the parts is full martensite and the micro-hardness is about HV 550 as the blanking temperature is in the range of 650-800℃. Furthermore, increasing the blanking temperature, the width of burnish zone increases.
Abstract: The transverse flow law of metals is very important for calculating the shape of steel strips during hot rolling. A metal elastic-plastic deformation model was developed using a general finite element software, ABAQUS. The calculation cost can be significantly reduced by imposing the transverse uniformity of the longitudinal displacement of the strip at the end face during steady rolling. The effect of factors on the transverse flow of metals and the effect of the transverse flow of metals on the shape of steel strips were analyzed using the developed model. Simulation results show that the effect of the friction condition of the contact interface on transverse flow is negligible. Moreover, during hot tandem rolling of wide steel strips, under the condition of constant unit crown, the variation of the width of the steel strip and fluctuation range of the mean front and back tension stresses do not affect the transverse flow and shape of metals. Further, the transverse flow of metals varies with the reduction ratio, which results in a trend toward the middle wave of the strip shape with the increase in the reduction ratio. It also varies with the similarity of the symmetric and asymmetric profiles and significantly reduces the effect of the change of profile similarity on the shape of the steel strip. A metal transverse flow prediction model is developed via the multivariate nonlinear regression method for online control, which lays the necessary foundation for strip shape regulation during hot rolling.
Abstract: The segmentation of metallographic images plays a key role in grain grading, but it is difficult to extract grains accurately using the traditional Chan-Vese (CV) model. To segment metallographic images more accurately, a metallographic image segmentation method based on an improved CV model was proposed. First, the level set function was initialized, and its reciprocal Canberra distance from inside and outside the curve was calculated. Then, these distances were used as weight coefficients of the fitting centers to restrain the influence of noise points on their accuracy. In addition, adding exponential entropy to adjust the energy inside and outside the curve reduces the influence of the fixed energy weight on the evolution of the curve. Lastly, to accelerate the convergence of the model, a distance-regularized term was introduced to avoid re-initialization of the level set function. The experimental results show that, compared with the traditional CV model, the geodesic active contour model, the distance-regularized level set evolution model, and the bias level correction level set model, the segmentation of the metallographic images based on the proposed model is more accurate and efficient, and the proposed model has better convergence.
Abstract: To achieve micro-scale roll gap shape adjustment, roll profile electromagnetic control technology was proposed and a φ270 mm×300 mm roll profile electromagnetic control experimental platform was designed and built. Meanwhile, a mathematical model based on electromagnetic, thermal and mechanical coupled parameters was established. The results of both the experiment and simulation were compared and analyzed under the same process conditions. The comparison shows that the experimental and simulated results are in the agreement, thus verifying the model. Based on the simulated results, the roll crown and the roll crown growth rate changing with heating time were calculated under different equivalent current densities and frequencies. The influence of current density, frequency and heating time on the roll profile curve was presented. In addition, reasonable technological parameters were used in order to avoid local overheating of the electromagnetic stick and further facilitate adjustment of the roll crown.
Abstract: A wavelet modulation strategy applied to a quasi-Z-source inverter was proposed. The regulating range of the shootthrough duty ratio could be increased by changing the locations of the sampling points set using traditional wavelet-modulation. The proposed modulation strategy divided the shoot-through zero vector into two portions, which were then individually inserted into both ends of the sampling time. Under the proposed strategy, the quasi-Z-source inverter could obtain a theoretical maximum constant shoot-through duty ratio without any extra switching frequencies. In addition, the proposed strategy was compared with traditional modulation strategies used in quasi-Z-source inverters. The boosting capacity, efficiency, harmonic and modulation ratio of the different modulation strategies for quasi-Z-source inverter were analyzed thoroughly. Finally, the performance of the proposed method was verified by simulation. Both the simulation results and theory verify that the strategy can reduce harmonic, increase voltage utilization rate, and enhance the boosting capacity.
Abstract: With the emergence of high dynamic range (HDR) images and videos, improving the liquid crystal display (LCD) technology has become an urgent requirement. The development of HDR display systems is becoming the focus of research in the display technology. To improve the dynamic range of LCDs to the best possible extent, a local dimming algorithm based on dynamicthreshold backlight luminance extraction and two-step liquid crystal pixel compensation was proposed to improve the dynamic range of a backlight model and an LCD panel, thereby enhancing the contrast and visual quality of the dimmed image. The experimental results demonstrate that the proposed algorithm can improve the image contrast ratio by approximately 113.60% on average. Additionally, on the direct white light-emitting diode backlight LCD, specific images were used to verify the accuracy of the proposed algorithm. The display effects indicate that the layering and color of dimmed images are enhanced and the image contrast ratio is improved. Based on these results, it can be concluded that the proposed algorithm can effectively improve both the contrast of LCDs and the display quality.
Abstract: The noninvasive measurement of multicore cables using space magnetic field analysis has characteristics of weak signal intensity, high sensitivity, and vulnerability to environmental or elemental interference. To calibrate the hard iron bias, soft iron bias, and scale factor of magnetoresistance sensors based on noninvasive measurements for multicore cables, a two-step estimation-based calibration method was proposed. This method establishes the error-related linear matrix equations through the nonlinear transformation of the sensor output signal and undertakes nonlinear regression calculation after solving the equations, thus implementing dynamic error correction for the measurement of multicore cable current. Results show that this method can simultaneously calibrate linear and partial nonlinear errors of noninvasive current measurement devices for multicore cables.
Abstract: To solve the problem of low precision control in high speed motion robots due to a time-varying payload and to improve the identification accuracy of the payload, the dynamical parameter identification methods for robot end payload were studied. These methods included the parameter difference method, the moment method, and the global parameter identification method. The parameters were used to improve the dynamic precision in robot dynamic control. The dynamical parameters for different payloads can be identified with the Lagrange dynamic linear identification model, which acquires real-time data using the optimal incentive path and solves the equations by using the least square weight algorithm after the sample data was processed with a low-pass filter and central difference processes. The feasibility of the method was verified by experiments.
Abstract: The performance of a walking mechanism determines whether a coal mine rescue robot can successfully enter a disaster scene for conducting a rescue. To explore which type of the crawler-walking mechanism is more suitable for the coal mine rescue robot, five types of common crawler-type walking mechanisms were evaluated based on the following four aspects:walking ability, explosion prevention, handling, and reliability. In the process of evaluation, the space pass capacity, the maximum obstacle height, the maximum trench width, and the chassis height of the five types of walking mechanisms were theoretically analyzed. Then, a mathematical model for determining the influence of the number of motor drives on the difficulty of explosion-proof, handling, and reliability was proposed. According to the design experience of the coal mine rescue robot and the theoretical model, the five types of walking mechanisms were quantitatively evaluated. Finally, the walking mechanism with the angle of entry and departure is found to be most suitable for the coal mine rescue robot. Based on the evaluation results, the CUMT-V coal mine rescue robot was designed.
Abstract: Task participants' malicious behavior can significantly reduce the credibility of mobile crowd sensing (MCS). To solve this problem, this paper proposed a data collection mechanism that analyzed and quantified participants' historical reputation according to their willingness and the quality of data they had shared, and then updated their current reputation through the logistic regression model. Simultaneously, to measure the authenticity of the collected data, the participants were divided into two types:those who were related to direct transmission of sensing data and second, those who were involved in indirect forwarding of these, which was based on the remaining transmission time of sensing data and residual energy of mobile equipment. Then the server analyzed the accuracy of data collected by participants according to the multitasking scenario. Simulation results show that the proposed mechanism can significantly improve the perceived tasks performed in real time, greatly upgrade the quality of sensing data, and effectively reduce the reward expenses.
Monthly, started in 1955 Supervising institution：Ministry of Education Sponsoring Institution：University of Science and Technology Beijing Editorial office：Editorial Department of Chinese Journal of Engineering Publisher：Science Press Chairperson：Ren-shu Yang Editor-in-Chief：Ai-xiang Wu ISSN 2095-9389CN 2095-9389
